1. Field of the Invention
The present invention relates generally to a cuff mechanism for blood pressure meters. More specifically, it relates to a finger cuff for an oscillometric sphygmomanometer.
The oscillometric method of determining blood pressure through detection of pulse oscillations was first reported by Roy and Adami in 1890. In the method, blood pressure is determined indirectly, as opposed to actually sticking a needle in the bloodstream, by occlusion of an artery by cuff pressurization. When cuff pressure is high enough to close an artery and thus stop the flow of blood, the pressure can be gradually released and compared to the blood flow returning to the artery. However, not until recently with the invention of computers and microprocessors has man been able to take advantage of this method.
2. Description of the Prior Art
The oscillometric method of determining blood pressure has traditionally involved mainly the optical oscillation method. In the optical oscillation method, a light emitting diode (LED) inside the cuff beams infrared light into the body. Since blood inside the artery absorbs more infrared than other living tissues, the amount of infrared that is exposed to a phototransistor (PTr) is a function of the blood volume in the artery. One disadvantage with this method is its reliance on light for measurement. Measurements conducted in daylight risk inaccuracy due to sunlight interfering with the infrared light. Another disadvantage with an optical oscillometric apparatus is that cuff construction for such a device is complicated and costly due to the infrared elements. Not only are the photoelectric devices expensive in and among themselves, but also they restrict bladder construction. The bladder construction must conform to the necessity of the photoelectric devices to be properly aligned with respect to the artery. Thus, bladders in the prior art contain many ridges which expand together in order to tighten the cuff. Although this allows the LED and the PTr to maintain proper alignment, the complex construction is more expensive and less effective than the simple bladder employed in this invention. First, the ridges reduce the accuracy of the measured blood pressure because the measurement is a function of the bladder's surface area contact with the skin. Secondly, the need for fitting all sizes of fingers necessitates a large initial diameter into which voluminous air pressure must be pumped.